The primary copper ore at the Peko mine, Tennant Creek, Northern Territory, Australia, contains about 9 per cent copper and 4.5 dwt. gold per ton. It is associated with a lens of magnetite rock, and consists of remnants of the magnetite rock in varying stages of replacement by pyrite, chalcopyrite, pyrrhotite, marcasite and minor amounts of wolframite, cobaltite, (?)safflorite, sphalerite, galena, bismuthinite, native bismuth, matildite, tetrahedrite, native gold, hematite and goethite (Edwards, 1955). The gangue minerals include quartz, siderite and chlorite.